You may have been told that humans vocal cords are not capable of this, and that is true. But there is a work around. A way to sort of emulate this sound using your tongue. Jinx figured out how to do this and would be happy to tell you how it's done. (And yes, he knows this is a silly skill to have.)

1) Take in a deep breath.

2) Slide your tongue up the roof of your mouth until it is just over the first ridge. (And Jinx does mean just over, any higher and this will not work correctly.)

3) Gently push your tongue into the roof of your mouth until you can just start to feel the pressure on the inside of your mouth. (You will feel it much more strongly on your tongue.)

4) Open your mouth just a tinny a bit.

5) Quickly start to exhale well relaxing your lips. You need to exhale fast enough that your lips do not close back up but not so fast that they push apart more. It may take you a few tries to get this just right.

If you practice you may find yourself learning to breath in though your nose and out though your mouth at the same time which will allow you to purr for much longer.